The taste bud is a useful model for the study of nerve-epithelial interactions during development and regeneration. Taste buds are notable because they have a trophic dependence upon their nerve supply---denervated taste buds will degenerate, but will reform if the nerve regenerates. This project examines the development and regeneration of taste buds and nerves in the tongue of rats and gerbils. Studies of Regeneration: Can gustatory axons find or be attracted to their proper locations if the axons return to the tongue by an abnormal route of entry? We will use an excess of gustatory axons to determine whether hyperinnervation of taste buds occurs and whether the gustatory epithelium has a hidden capacity to form more taste buds or receptor cells. Competitive interactions between two gustatory nerves, both native and foreign to the region, will be examined. Studies of Development: We will examine the development of rodent taste buds to determine if a nerve supply is necessary for the initial formation of taste buds, and whether there is a critical period in establishing gustatory competence. We will also determine whether embryonic regulation can occur in a region previously containing gustatory epithelium and whether the absence of target gustatory epithelium in development leads to neuronal cell death. We will evaluate the residual trophic competence of gustatory epithelium and gustatory nerves after a developmental history of reduced nerve-epithelial interactions which has led to a permanent failure of taste bud development. In summary we will use electrophysiological and morphological assays to reveal some of the important principles which facilitate receptor and neuronal development and regeneration.